Blood Pressure

A patients systolic blood pressure was identified as playing a critical role in the secondary brain injury cascade as early as 1989¹⁰, when a study reported a 35% mortality in patients admitted with a SBP <85mmHg, compared with 6% in patients with higher SBP¹⁰. In addition, hypotension has been shown to correlate with diffuse brain swelling¹¹. If autoregulation remains intact, a drop in SBP triggers an autoregulatory vasodilation in an attempt to maintain cerebral perfusion. This results in an increased cerebral blood volume, which in turn elevates ICP. If autoregulation is not intact e.g., due to a TBI, there is a dependency on a sufficiently high SBP to prevent cerebral ischaemia occurring as a secondary insult¹².

Previous iterations of the BTF guidelines used the traditional definition of hypotension as a SBP <90mmHg^13,14. However, the literature now supports a higher level that may vary with pre-morbid state or age, as concluded by Berry et al¹⁵ and supported by two subsequent studies^16-17, which suggested maintenance of higher blood pressures might result in better outcomes^15,16,17. The 2016 BTF recommendations suggest maintaining a SBP at 100mmm Hg for patients 50-69 years old or 110mm HG for patients 15-49 or >70 years old may decrease mortality and improve outcomes¹⁸.